In-mold coating involves the use of a film from which a shell is formed corresponding to the shape of one half a pressure mold, usually the cavity, by conventional thermoforming, or by using the pressure mold cavity itself as the thermoforming tool. If the latter, the film may be preheated and formed in that cavity, with the formed shell juxtaposed with the other mold half, to form a plastic molded part therein. Alternately, the film may be clamped against one parting face of a pressure mold and the plastic molded against it, whereby the latter softens the film and forces it into the cavity of course, the film may also be preheated before the pressure molding step.
Whichever procedure is followed, a laminated pressure molded plastic article is formed with a skin consisting of the film. The skin may be colored or decorated to provide a decorated or color coated article.
It is highly desirable to provide an improved process for forming a color coated article of the aforesaid type. The cost of the film and the process of introducing it into the pressure mold represent major parts of the total cost of applying a finish to the pressure molded article in the foregoing procedure.
Further, as described above, the shell is formed by thermoforming, whether in a separate mold, or in the pressure molding cavity. Thus, it is drawn from a sheet that is typically large enough to accommodate the formation of several shells at the same time, meaning that several thermoforming mold cavities must be placed in juxtaposition with the sheet. This, in turn, leaves spaces between the cavities covered by film stock not used to make shells and is thus wasted. The shells so formed are then punched out of one sheet, to be placed into the pressure molding cavities, and the rest of the expensive sheet, the so-called "skeleton scrap", is discarded.
When the shell is formed in the pressure molding cavities of multi-impression molds, the amount of skeleton scrap is greater than for thermoforming done separately, because the spacing of cavities in thermoforming is closer than in pressure molding of molten plastic.
With separately thermoformed shells, an additional problem arises when attempting to place the shells into the pressure molding cavity accurately enough to avoid folds and other defects due to the pressure molding step.
In addition, when the plastic is molded against the film, it is desirable to obtain a good bond between the molded plastic and the film without the added expense and inconvenience of bonding aids and the like in order to avoid unbonded sites and even delamination. This may represent a significant problem.
Accordingly, it is a principal object of the present invention to provide an improved process for forming a color coated article using in-mold coating.
It is a further object of the present invention to provide an improved process as aforesaid which minimizes scrap formation and defects in processing.
It is a still further object of the present invention to provide a process as aforesaid which is economical and easy to use.
It is a further object of the present invention to provide a process as aforesaid which obtains a good bond between the molded plastic and the film without the necessity for expensive and inconvenient bonding aids and the like.
Further objects and advantages of the present invention will appear hereinbelow.